pwm: Allow store 64-bit duty cycle from sysfs interface

PWM core was converted to u64 by the commit a9d887dc ("pwm: Convert
period and duty cycle to u64") but did not change the duty_cycle_store()
so it will error out if trying to pass a numeric string bigger than
2^32-1.

Fix this by using u64 and kstrtou64() in duty_cycle_store().
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Guru Das Srinagesh <gurus@codeaurora.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/sysfs.c

@@ -87,10 +87,10 @@ static ssize_t duty_cycle_store(struct device *child,
 	struct pwm_export *export = child_to_pwm_export(child);
 	struct pwm_device *pwm = export->pwm;
 	struct pwm_state state;
-	unsigned int val;
+	u64 val;
 	int ret;
 
-	ret = kstrtouint(buf, 0, &val);
+	ret = kstrtou64(buf, 0, &val);
 	if (ret)
 		return ret;